How to maintain IK chain angle to target?
If I am understanding your question correctly, I think this kind of setup would be the simplest solution:



The main point is to disable "Inherit Rotation" for the tip bone.



Extrude another bone from the root of the "Tip Bone" that will be the "IK Target", and clear its Parent (AltP in Armature Edit Mode). It must not have a Parent in order to function properly as an IK Target.